Wavelength stabilizer for TWDM-PON burst mode DBR laser

ABSTRACT

An optical network unit (ONU) comprising a media access controller (MAC) configured to support biasing a laser transmitter to compensate for temperature related wavelength drift receiving a transmission timing instruction from an optical network control node, obtaining transmission power information for the laser transmitter, estimating a burst mode time period for the laser transmitter according to the transmission timing instruction, and calculating a laser phase fine tuning compensation value for the laser transmitter according to the burst mode time period and the transmission power information, and forwarding the laser phase fine tuning compensation value toward a bias controller to support biasing a phase of the laser transmitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/514,080, filed Oct. 14, 2014 by Feng Wang et al., andentitled “Wavelength Stabilizer For TWDM-PON Burst Mode DBR Laser,”which claims priority to U.S. Provisional Patent Application 61/890,689,filed on Oct. 14, 2013 by Feng Wang et al., and entitled “WavelengthStabilizer For TWDM-PON Burst Mode DBR Laser,” which is incorporatedherein by reference as if reproduced in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Time and wavelength division multiplexing (TWDM) passive optical network(PON) systems are multi-wavelength systems for upstream and downstreamdirection communications. Different channels are transmitted by a laserdiode, typically in an optical network unit (ONU), via opticalconnections (e.g., optical fibers) to a destination receiver. Ade-multiplexer at a central office separates upstream wavelengths intodifferent channels.

SUMMARY

In one embodiment, the disclosure includes an ONU comprising a mediaaccess controller (MAC) configured to support biasing a lasertransmitter to compensate for temperature related wavelength driftreceiving a transmission timing instruction from an optical networkcontrol node, obtaining transmission power information for the lasertransmitter, estimating a burst mode time period for the lasertransmitter according to the transmission timing instruction, andcalculating a laser phase fine tuning compensation value for the lasertransmitter according to the burst mode time period and the transmissionpower information, and forwarding the laser phase fine tuningcompensation value toward a bias controller to support biasing a phaseof the laser transmitter.

In another embodiment, the disclosure includes a method of biasing aphase of a laser transmitter to compensate for temperature relatedwavelength drift implemented in an optical device, wherein the methodcomprises receiving a transmission timing instruction from an opticalline terminal (OLT), wherein the transmission timing instructionindicates a timeslot for an upstream transmission by the lasertransmitter, estimating a laser transmitter burst mode time period basedon the timeslot calculating transmission power information based on ameasurement of current associated with the laser transmitter,calculating an amount of injection current to be used for biasing thephase of the laser transmitter phase based on the calculatedtransmission power information and the estimated burst mode time period,and biasing the laser transmitter to compensate for temperature relatedwavelength drift by injecting the calculated injection current into aninput of a Distributed Bragg Reflector (DBR) laser gain section of thelaser transmitter concurrently with data input.

In yet another embodiment, the disclosure includes a method implementedin a PON comprising transmitting an optical signal in the PON via alaser transmitter utilizing TWDM, and compensating for a red-shift in awavelength of the optical signal associated with an increase intemperature of the laser transmitter associated with a duration of anoptical signal burst, wherein compensation is performed by introducing ablue-shift wavelength bias to the DBR laser gain section of the lasertransmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of a PON.

FIG. 2 is a schematic diagram of an embodiment of a network element.

FIG. 3 is a schematic diagram of an embodiment of an ONU.

FIG. 4 is a schematic diagram of a DBR laser.

FIG. 5 is a flowchart of an embodiment of a method of biasing a phase ofa laser transmitter.

FIG. 6 is a flowchart of an embodiment of a method for transmitting ablue-shift compensated optical signal in a PON.

FIG. 7 is a schematic diagram of a TWDM-PON architecture.

FIG. 8 is a graph of data relating laser transmission wavelength innanometers (nm) and laser diode temperature in degrees Celsius (C.°).

FIG. 9 is a graph of data associated with an embodiment of a TWDM-PONONU transmitter architecture.

FIG. 10 is a graph of wavelength shift versus optical power transmissionpower for various burst mode time periods for an embodiment of anuncompensated ONU transmitter.

FIG. 11 is a graph of DBR tunable laser section tuning current versuswavelength.

FIG. 12 is a graph of laser phase section tuning current versuswavelength.

FIG. 13 is a graph of laser temperature associated with an ONU employingDBR laser wavelength stabilization.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Disclosed herein is a transmitter that is wavelength insensitive toburst length and is employed in an ONU in a TWDM-PON. The transmittercompensates for wavelength drift caused by temperature shifts associatedwith varying burst lengths in a DBR laser. The ONU compensates forwavelength drift by employing a media access controller block to providelaser phase fine tuning current value according to a control algorithm.A tuning current is generated according to the laser phase fine tuningcurrent value and is used to stabilize the laser wavelength. Thetransmitter is employed to provide wavelength stabilization to supportreal-time bandwidth assignment and traffic management, and is capable ofdynamic upstream transmission stabilization.

FIG. 1 is a schematic diagram of an embodiment of a PON 100. The PON 100comprises an OLT 110, a plurality of ONUs 120; and an ODN 130, which maybe coupled to the OLT 110 and the ONUs 120. The PON 100 comprises acommunications network that does not require any active components todistribute data between the OLT 110 and the ONUs 120. Instead, the PON100 uses passive optical components in the ODN 130 to distribute databetween the OLT 110 and the ONUs 120. In one embodiment, the PON 100comprises a Next Generation Access (NGA) system, such as a ten GbpsGigabit PON (XGPON), which has a downstream bandwidth of about ten Gbpsand an upstream bandwidth of at least about 2.5 Gbps. Alternatively, inanother embodiment, the PON 100 comprises any Ethernet based network,such as an Ethernet Passive Optical Network (EPON) defined by theInstitute of Electrical and Electronics Engineers (IEEE) 802.3ahstandard, a 10 Gigabit EPON as defined by the IEEE 802.3av standard, anasynchronous transfer mode PON (APON), a broadband PON (BPON) defined bythe International Telecommunication Union (ITU) TelecommunicationStandardization Sector (ITU-T) G.983 standard, a Gigabit PON (GPON)defined by the ITU-T G.984 standard, a wavelength division multiplexed(WDM) PON (WPON), or a suitable after-arising technology, all of whichare incorporated herein by reference as if reproduced in their entirety.

In an embodiment, the OLT 110 comprises any devices configured tocommunicate with the ONUs 120 and another network (not shown).Specifically, the OLT 110 acts as an intermediary between the othernetwork and the ONUs 120. For instance, the OLT 110 forwards datareceived from the network to the ONUs 120, and forwards data receivedfrom the ONUs 120 onto the other network via a system network interface(SNI). Although the specific configuration of the OLT 110 may varydepending on the type of PON 100, in one embodiment, the OLT 110comprises a transmitter and a receiver, a wavelength divisionmultiplexing multiplexer (WDM MUX) for multiplexing signals over aplurality of wavelengths, and a media access controller (MAC) forcontrolling packet encoding/decoding on an optical signal. When theother network uses a network protocol, such as Ethernet or SynchronousOptical Networking/Synchronous Digital Hierarchy (SONET/SDH), whichdiffers from the PON protocol used in the PON 100, the OLT 110 furthercomprises a converter that converts the network protocol into the PONprotocol. The OLT 110 converter also converts the PON protocol into thenetwork protocol. The OLT 110 is typically located at a centrallocation, such as a central office, but may be located at otherlocations as well in alternative embodiments.

In an embodiment, the ONUs 120 comprise any devices that are configuredto communicate with the OLT 110 and a customer or user via a usernetwork interface (UNI). Specifically, the ONUs 120 acts as anintermediary between the OLT 110 and the customer. For instance, theONUs 120 forwards data received from the OLT 110 to the customer andforwards data received from the customer onto the OLTs 110. Although thespecific configuration of the ONUs 120 may vary depending on the type ofPON 100, in one embodiment, the ONUs 120 comprise an optical transmitterconfigured to send optical signals to the OLT 110, an optical receiverconfigured to receive optical signals from the OLT 110, and a MAC forcontrolling packet encoding/decoding. In some embodiments, the opticalsignals are sent in a burst mode. In embodiments in which a pluralityoptical signals sharing a common wavelength are to be sent, the opticalsignals employ a common transmission channel. Additionally, the ONUs 120further comprise a converter that converts the optical signal intoelectrical signals for the customer, such as signals in the Ethernet orasynchronous transfer mode (ATM) protocol, and a second transmitterand/or receiver that sends and/or receives the electrical signals toand/or from a customer device. In some embodiments, ONUs 120 and opticalnetwork terminals (ONTs) are similar, and thus the terms are usedinterchangeably herein. The ONUs 120 is typically located at distributedlocations, such as the customer premises, but may be located at otherlocations as well in alternative embodiments.

In an embodiment, the ODN 130 comprises a data distribution system,which comprises optical fiber cables, couplers, splitters, distributors,and/or other equipment. In an embodiment, the optical fiber cables,couplers, splitters, distributors, and/or other equipment comprisepassive optical components. Specifically, the optical fiber cables,couplers, splitters, distributors, and/or other equipment are componentsthat do not require any power to distribute data signals between the OLT110 and the ONUs 120. Alternatively, in another embodiment, the ODN 130comprises one or a plurality of active components, such as opticalamplifiers. The ODN 130 typically extends from the OLTs 110 to the ONUs120 in a branching configuration as shown in FIG. 1, but in alternativeembodiments may be alternatively configured in any otherpoint-to-multi-point configuration.

At least some of the features/methods described in this disclosure areimplemented in a network element. For instance, the features/methods ofthis disclosure may be implemented using hardware, firmware, and/orsoftware installed to run on hardware. FIG. 2 is a schematic diagram ofan embodiment of a network element 200 that may act as an ONU 120 and/orOLT 110, each shown in FIG. 1. The network element 200 is any device(e.g., an access point, an access point station, a router, a switch, agateway, a bridge, a server, a client, a user-equipment, a mobilecommunications device, ONU, ONT, OLT, etc.) that transports and/orfacilitates transmission of data through a network, system, and/ordomain.

The network element 200 comprises one or more downstream ports 210coupled to a transceiver (Tx/Rx) 220, which comprise transmitters,receivers, or combinations thereof. The Tx/Rx 220 transmits and/orreceives frames from other network nodes via the downstream ports 210.Similarly, the network element 200 comprises another Tx/Rx 220 coupledto a plurality of upstream ports 240, wherein the Tx/Rx 220 transmitsand/or receives frames from other nodes via the upstream ports 240. Thedownstream ports 210 and/or the upstream ports 240 include electricaland/or optical transmitting and/or receiving components. Further, notall of the downstream ports 210 and/or the upstream ports 240 need bethe same type in some embodiments (e.g. some electrical ports, someoptical ports, etc.). In another embodiment, the Tx/Rx 220 comprises oneor more laser diodes, such as a Transmitter Optical Sub-Assembly (TOSA),one or more photoreceptors, such as a Receiver Optical Sub-Assembly(ROSA), or combinations thereof. In some embodiments, the laser diodesare DBR laser diodes in a TWDM-PON architecture. The Tx/Rx 220 may alsotransmit and/or receive data (e.g., packets) from other network elementsvia wired or wireless connections, depending on the embodiment.

In some embodiments, the Tx/Rx 220 comprise a MAC module 260. The MACmodule 260 is implemented via execution by processor 230, memory 250,Tx/Rx 220, and/or combinations thereof. In one embodiment, the MACmodule 260 is implemented according to embodiments of the presentdisclosure to determine a tuning current and/or compensation currentvalue for a laser diode coupled directly or indirectly to MAC module260. In some embodiments the Tx/Rx 220 further comprise a bias controlmodule 270. The bias control module 270 is implemented via execution byprocessor 230, memory 250, Tx/Rx 220, and/or combinations thereof. Inone embodiment, the bias control module 270 is implemented to provide alaser diode with a tuning current and/or compensation current accordingto a value determined by MAC module 260. The bias control module 270and/or MAC module 260 may be employed to implement methods 500 and 600,as discussed herein below, as well as any other methods disclosedherein. In some embodiments, MAC module 260 and bias control module 270are stored in memory 250 and are accessed and/or executed viainstructions from processor 230 and/or Tx/Rx 220.

A processor 230 is coupled to the Tx/Rx 220 and is configured to processthe frames and/or determine to which nodes to send (e.g., transmit) thepackets. In an embodiment, the processor 230 comprises one or moremulti-core processors and/or memory modules 250, which function as datastores, buffers, etc. The processor 230 is implemented as a generalprocessor or as part of one or more application specific integratedcircuits (ASICs), field-programmable gate arrays (FPGAs), and/or digitalsignal processors (DSPs). Although illustrated as a single processor,the processor 230 is not so limited and may comprise multipleprocessors. The processor 230 is configured to communicate and/orprocess multi-destination frames.

FIG. 2 illustrates that a memory module 250 is coupled to the processor230 and is a non-transitory medium configured to store various types ofdata and/or instructions. Memory module 250 comprises memory devicesincluding secondary storage, read-only memory (ROM), and random-accessmemory (RAM). The secondary storage is typically comprised of one ormore disk drives, optical drives, solid-state drives (SSDs), and/or tapedrives and is used for non-volatile storage of data and as an over-flowstorage device if the RAM is not large enough to hold all working data.The secondary storage is used to store programs which are loaded intothe RAM when such programs are selected for execution. The ROM is usedto store instructions and perhaps data that are read during programexecution. The ROM is a non-volatile memory device which typically has asmall memory capacity relative to the larger memory capacity of thesecondary storage. The RAM is used to store volatile data and perhaps tostore instructions. Access to both the ROM and RAM is typically fasterthan to the secondary storage.

It is understood that by programming and/or loading executableinstructions onto the network element 200, at least one of the processor230, the cache, and the long-term storage are changed, transforming thenetwork element 200 in part into a particular machine or apparatus, forexample, a multi-core forwarding architecture having the novelfunctionality taught by the present disclosure. It is fundamental to theelectrical engineering and software engineering arts that functionalitythat can be implemented by loading executable software into a computercan be converted to a hardware implementation by well-known design rulesknown in the art. Decisions between implementing a concept in softwareversus hardware typically hinge on considerations of stability of thedesign and number of units to be produced rather than any issuesinvolved in translating from the software domain to the hardware domain.Generally, a design that is still subject to frequent change may bepreferred to be implemented in software, because re-spinning a hardwareimplementation is more expensive than re-spinning a software design.Generally, a design that is stable and will be produced in large volumemay be preferred to be implemented in hardware (e.g., in an ASIC)because for large production runs the hardware implementation may beless expensive than software implementations. Often a design may bedeveloped and tested in a software form and then later transformed, bywell-known design rules known in the art, to an equivalent hardwareimplementation in an ASIC that hardwires the instructions of thesoftware. In the same manner as a machine controlled by a new ASIC is aparticular machine or apparatus, likewise a computer that has beenprogrammed and/or loaded with executable instructions may be viewed as aparticular machine or apparatus.

Any processing of the present disclosure may be implemented by causing aprocessor (e.g., a general purpose multi-core processor) to execute acomputer program. In this case, a computer program product can beprovided to a computer or a network device using any type ofnon-transitory computer readable media. The computer program product maybe stored in a non-transitory computer readable medium in the computeror the network device. Non-transitory computer readable media includeany type of tangible storage media. Examples of non-transitory computerreadable media include magnetic storage media (such as floppy disks,magnetic tapes, hard disk drives, etc.), optical magnetic storage media(e.g., magneto-optical disks), compact disc read-only memory (CD-ROM),compact disc recordable (CD-R), compact disc rewritable (CD-R/W),digital versatile disc (DVD), Blu-ray (registered trademark) disc (BD),and semiconductor memories (such as mask ROM, programmable ROM (PROM),erasable PROM, flash ROM, and RAM). The computer program product mayalso be provided to a computer or a network device using any type oftransitory computer readable media. Examples of transitory computerreadable media include electric signals, optical signals, andelectromagnetic waves. Transitory computer readable media can providethe program to a computer via a wired communication line (e.g., electricwires, and/or optical fibers) and/or a wireless communication line.

FIG. 3 is a schematic diagram of an embodiment of an ONU 300, which maybe substantially similar to ONUs 120 and/or implemented in networkelement 200, for example in Tx/Rx 220. In alternative embodiments of ONU300, the ONU 300 may be an optical network terminal (ONT). ONU 300comprises a receiver 360, a media access controller (MAC) 310, biascontroller 320, DBR laser 330, photodiode (PD) 340, and analog todigital converter (ADC) 350. ONU 300 is configured to compensate forwavelength shift in DBR laser 330 to minimize deviation from DBR laser330's central peak wavelength. In some embodiments, ONU 300 compensatingfor the wavelength shift is known as introducing a blue-shift.

PD 340 is a detector configured to couple to DBR laser 330 and captureand/or measure a portion of the transmission power of DBR laser 330 asan analog value. After capturing and/or measuring a portion of thetransmission power of DBR laser 330, PD 340 forwards the analogtransmission power information to ADC 350. After receiving the analogtransmission power information from PD 340, ADC 350 converts the analogtransmission power information to a digital value and transmits thedigital transmission power information to MAC 310.

Receiver 360 may receive downstream timeslot information from a source(e.g., an OLT, such as OLT 110). The receiver 360 forwards thedownstream timeslot information and/or instructions to a processor (e.g.processor 230), a storage device (e.g. memory module 250), and/or theMAC 310. The MAC 310 estimates a burst mode time period of ONU 300 basedon the downstream timeslot information/instructions and/or based on userdata for upstream communication (e.g. received from a user, processor,storages device, etc.). The burst mode time period indicates a period oftime that corresponds to an output transmission of DBR laser 330. Insome embodiments the timeslot information and/or instructions arereceived from an OLT, such as OLT 110, shown in FIG. 1. It should benoted that some or all of the timeslot information and/or instructionsmay be received from other components in the ONU 300 (e.g. configuredbased on user initiated communications and known timeslot informationfrom an OLT). According to the estimated burst mode time period, as wellas digital transmission power information received from ADC 350, MAC 310determines a laser phase fine tuning current value for DBR laser 330. Insome embodiments, the laser phase fine tuning current value is a timedependent function such that it is defined by I_(p)=f(t), where I_(p) isthe phase current and t represents time and ranges from 0 to the end ofthe burst mode time period. After determining the laser phase finetuning current value, MAC 310 transmits the value to bias controller 320to enable the injection of the laser phase fine tuning current into DBRlaser 330 to compensate for wavelength shift associated with burst modetemperature shifts when DBR laser 330 is enabled, thereby causing theoutput of DBR 330 to experience a net wavelength shift of about zero.

Bias controller 320 comprises an electronic control circuit configuredto provide DBR laser 330 with the laser phase fine tuning current. Thelaser phase fine tuning current is utilized to force a blue-shift in DBRlaser 330 to compensate for a temperature associated red-shift inupstream transmissions from DBR laser 330. Bias controller 320determines the laser phase fine tuning current according to the laserphase fine tuning value received from MAC 310.

DBR laser 330 is configured to receive digital user data from adownstream source (e.g., a client device) and transmit the digital datato an upstream destination (e.g., an OLT). In some embodiments, thedigital data received by DBR laser 330 is represented by an electricalcurrent. To transmit the digital data to the upstream source, DBR laser330 converts the digital data into optical data (e.g., light). In someembodiments, DBR laser 330 combines a tuning current (e.g., the laserfine tuning current) received from a controller (e.g., bias controller320) with the optical data to form an output transmission of DBR laser330. In some embodiments of ONU 300, upstream wavelength stabilizationis employed to automatically adjust the working wavelength of atransmission module (e.g., a laser such as DBR laser 330) to match thegrid wavelength of a de-multiplexer in an associated OLT.

FIG. 4 is a schematic diagram of a DBR laser 400, which may besubstantially similar to DBR laser 330. DBR laser 400 comprises a DBRtuning section 410, a phase tuning section 420, a gain section 430, aphotodiode (PD) 460, a sub-mount 470, a thermoelectrically cooling (TEC)module 480, and an optical output 490. DBR laser gain section 430aggregates an Radio Frequency (RF) input and a bias input to generate atotal input signal that is encoded onto an optical signal fortransmission to an upstream destination by DBR laser 400. The RF inputcomprises user data received by DBR laser 400 for sending to an upstreamdestination via an optical signal, which in some embodiments may be aburst mode transmission. The bias input is used to introduce acompensation value to the output of DBR laser 400, for example ablue-shift wavelength compensation for a corresponding red-shiftexperienced by DBR laser 400 as a result of temperature increases, as isdiscussed below in greater detail. In some embodiments of DBR laser 400phase tuning section 420 controls and/or manipulates a phase of theoptical signal and may also be used to compensate for red-shift cause byburst mode operation. Gain section 430 controls a transmission strengthof the optical signal generated by DBR laser 400 by increasing an amountof power of the optical signal for transmission. In some embodiments ofa DBR laser 400, a plurality of output facets are provided. In someembodiments, current is applied to DBR tuning section 410 to performwide range wavelength tuning. A first output facet is coupled to anoptical fiber for transmitting optical signals to an upstream and/ordownstream destination. A second output facet is coupled to PD 460. Inembodiments of DBR laser 400 that employ PD 460, the PD 460 comprises adetector that detects and/or measures the output power of the lasertransmitter in order to monitor optical signals generated by DBR laser400. The DBR laser is mounted to TEC module 480 via sub-mount 470, whichacts as a structural component and/or heat sink. TEC module 480 isconfigured to perform cooling operations for DBR laser 400 by acting asa solid state heat pump to further reduce temperature related wavelengthdrift.

When DBR laser 400 performs a burst mode transmission, the wavelength ofthe associated tunable laser shifts due to temperature drift during theburst mode transmission. As used herein, an increase in wavelength maybe referred to as a red-shift and a decrease in wavelength may bereferred to as a blue-shift. The shift in upstream wavelength results inperformance degradation in the system because, for a multi-wavelengthTWDM-PON system (e.g., architecture 100, shown in FIG. 1), thede-multiplexer (e.g., at OLT 110, shown in FIG. 1) is employed toseparate upstream wavelengths into their respective receiving channelsat a central office. Deviation from the central peak wavelength for atransmission increases the power requirements for compensation at thede-multiplexer.

FIG. 5 is a flowchart of an embodiment of a method 500 of biasing aphase of a laser transmitter (e.g., a DBR, such as DRB laser 330, shownin FIG. 3). In some embodiments, method 500 is implemented in an ONU,such as ONU 300 and/or network element 200. At step 510, a transmissiontiming instruction is received from a source. The transmission timinginstruction indicates a timeslot for upstream optical signaltransmissions from the laser transmitter. In some embodiments, thetransmission timing instruction is received by a MAC, such as MAC 310,shown in FIG. 3. At step 520, a burst mode time period for the lasertransmitter is estimated based on the received transmission timinginformation. In some embodiments, the estimation of the burst mode timeperiod is determined by the MAC. At step 530, transmission powerinformation for the laser transmitter is calculated based on ameasurement of current associated with the laser transmitter. In someembodiments, the MAC performs the calculation of the transmission powerinformation based on a digital current value received via measurement bya photodiode. At step 540, an amount of injection current for biasingthe laser transmitter is determined based on the estimated burst modetime period and calculated transmission power information. In someembodiments, the amount of injection current is determined by the MAC.The amount of injection current is in some embodiments referred to as ablue-shift and/or a compensation current. At step 550, a DBR gainsection of the laser transmitter is biased with the injection current tocompensate for wavelength drift in the laser transmitter output that iscaused by an increase in temperature associated with the lasertransmitter. In some embodiments, the laser transmitter is biased by abias controller, such as bias controller 320 according to instructions(e.g., the injection current determined in step 540) received from theMAC.

FIG. 6 is a flowchart of an embodiment of a method 600 for transmittinga blue-shift compensated optical signal in a PON such as PON 100, shownin FIG. 1. In some embodiments, method 600 is implemented by an ONU,such as ONU 400 and/or network element 200. At step 610, an opticalsignal is transmitted via a laser transmitter, such as DBR laser 330,shown in FIG. 3. At step 620, the transmission of step 610 isdynamically compensated to adjust for a red-shift in the transmissionwavelength. In some embodiments, the red-shift in the transmissionwavelength is associated with a duration of an optical signal burst fromthe laser transmitter. To compensate for the red-shift in thetransmission wavelength, a blue-shift bias is introduced to a DBR lasergain section of the laser transmitter.

FIG. 7 is a schematic diagram of a TWDM-PON architecture 700 which canbe used to implement a network such as PON 100, shown in FIG. 1.Architecture 700 comprises an ONU 710, which may be substantiallysimilar to ONU 120, shown in FIG. 1, coupled to an OLT 720, which may besubstantially similar to OLT 110, shown in FIG. 1, via one or moreoptical connections 730 that utilize optical fibers. In someembodiments, ONU 710 and OLT 720 each comprise a ROSA 740 for receivingoptical transmissions, a TOSA 750 for transmitting optical signals, anoptical splitter assembly (OSA) for splitting/combining optical signals(e.g. a 1:2 coupler), as well as attenuators 760. In other embodiments,ONU 710 further comprises a miniature device (XMD) TOSA package tunablelaser. Architecture 700 is used to determine laser (e.g., aThermoelectrically cooled (TEC) laser and/or a DBR laser) wavelengthdrift. TEC lasers experience wavelength drift, as discussed above withrespect to FIG. 4, due to changes in the laser diode that occur as aresult of heat. During burst mode transmissions, the temperature of theTEC laser chip increases in a short period of time, resulting in thewavelength drift.

FIG. 8 is a graph 800 of data relating laser transmission wavelength innanometers (nm) and laser diode temperature in C.°. The data of FIG. 8is obtainable as results from an embodiment of architecture 700. Asshown in FIG. 8, the transmission wavelength of an uncompensated DBRlaser shifts as temperature increases. Specifically, over the range of 0C.° to 60 C.°, the laser wavelength experiences a red-shift of about 8nm. In some embodiments, the wavelength hops several times within atemperature range of 0 C.° to 60 C.°. A DBR laser operating in burstmode experiences hopping when the laser mode shift rate caused bytemperature change is different from an associated DBR reflectionspectral profile shift rate.

FIG. 9 is a graph 900 of data associated with an embodiment of aTWDM-PON ONU transmitter architecture, such as architecture 700, shownin FIG. 7. When a TEC is set to about 45 C.° and the ONU bandwidth isheld at 100 Megabits per second (Mbps), the wavelength remains at aboutwavelength unit (λ1). When the bandwidth increases from 100 Mbps to 2.5Gigabits per second (Gbps) (e.g. full bandwidth), the wavelength shiftsto about a second wavelength unit (λ2). The shifting time occurs inabout 1 second (s). When the wavelength shifts from λ1 to λ2, thewavelength deviates from its ideal peak value and results in losscausing a reduced power budget for the architecture.

FIG. 10 is a graph 1000 of wavelength shift in gigahertz (GHz) versusoptical transmission power (P_(tx)) in Decibel-milliwatts (dBm) forvarious burst mode time periods in microseconds (μs) for an embodimentof an uncompensated ONU transmitter, such as ONU 120, shown in FIG. 1,operating in a PON, such as PON 100, shown in FIG. 1. When an ONUtransmits in burst mode, a red-shift is observed in the resultingtransmission. As burst mode time periods increase, laser diodetemperature increases accordingly. As shown in graph 1000, the red-shiftis reduced when transmission power and/or the burst mode time period arereduced. In some embodiments, a reduction in transmission powercorresponds to a reduction in the optical power budget of upstreamtransmissions from the ONU. In other embodiments, a reduction in theburst mode time period reduces upstream bandwidth in an architecturesuch as PON 100, shown in FIG. 1, that includes the ONU. As a result ofde-multiplexer filter characteristics, red-shift in a transmission fromthe ONU causes upstream channel loss to vary with burst length. Tocompensate for the red-shift, a DBR laser fine tuning can be employedaccording to embodiments of ONU 300, disclosed above in FIG. 3, to causethe laser wavelength to blue-shift. Such a blue-shift compensates forthe red-shift and results in a net shift of zero in an ONU outputtransmission.

FIG. 11 is a graph 1100 of DBR tunable laser DBR section current inmilliamps (mA) versus wavelength in nm. In some embodiments, the resultsof FIG. 11 are obtainable through implementation of a system forcompensating for wavelength red-shift caused by increased temperature,for example, a red-shift in the output of DBR laser 330 in ONU 300and/or in a Tx/Rx 220 of network element 200. As DBR section currentincreases and a wavelength of the DBR laser experiences a blue-shift,the DBR laser hops one or more times from a first mode to a second mode.Each wavelength mode hop is about 0.7 nm, and is determined by theparticular design of the DBR laser being utilized. As a result of themode hops in the wavelength, the wavelength does not provide continuoustuning for a DBR laser.

FIG. 12 is a graph 1200 of laser phase fine tuning current versuswavelength. In some embodiments, the results of FIG. 12 are obtainablethrough implementation of a system for compensating for wavelengthred-shift caused by increased temperature, such as, for example, ared-shift in the output of DBR laser 330 in ONU 300, both shown in FIG.3. As laser phase section current increases, a wavelength of the DBRlaser experiences a blue-shift. The blue-shift of the wavelengthcomprises a tuning curve capable of continuously tuning the DBR laser.As shown in FIG. 12, the wavelength of the DBR laser changes cyclicallyas laser phase fine tuning current increases.

In order to stabilize the DBR laser wavelength despite temperaturechange, the DBR laser gain section may be biased at some calculatedvalue which may compensate for laser chip temperature increasing and/ordecreasing for a particular application case. For example, when a DBRlaser experiences a red-shift due to temperature increases, such as thered-shift illustrated in FIG. 8, injection current corresponding to FIG.11 and FIG. 12, respectively, are provided to the DBR laser gain sectionto cancel the red-shift with a blue-shift, resulting in a net wavelengthshift substantially close to zero.

FIG. 13 is a graph 1300 of laser temperature associated with an ONU,such as ONU 300, shown in FIG. 3, employing DBR laser wavelengthstabilization by applying a blue-shift bias to a DBR tuning section. ADBR laser utilizing the laser phase fine tuning of the presentdisclosure stabilizes a wavelength to within about ±0.1 nm of an optimalvalue for a laser diode changing from 10 C.° to 50 C.°. As shown in FIG.13, a 2.5 Gigahertz (GHz) modulation for DBR laser wavelengthstabilization at an ONU is measured. For varying burst mode timeperiods, blue-shift compensation in the DBR laser varies correspondingly(e.g., a longer burst mode time period results in a greater laser diodetemperature increases and red-shift, thereby requiring a greaterblue-shift). In some embodiments the blue-shift compensation is referredto as laser phase fine tuning, and has a rapid response rate (e.g.,about 10 nanoseconds (ns)). At small temperature changes (e.g., an about1 C.° to about 0.5 C.° temperature change), wavelength stabilizationerror is less than 0.01 nm. At larger temperature changes (e.g., about40 C.°) wavelength stabilization error is improved through the use of ahigh resolution current source.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method implemented in a passive optical network (PON) comprising: transmitting an optical signal in the PON via a laser transmitter utilizing time and wavelength division multiplexing (TWDM); and dynamically compensating for a red-shift in a wavelength of the optical signal by introducing a blue-shift wavelength bias to a phase section of the laser transmitter, wherein the red-shift is associated with an increase in temperature of the laser transmitter, wherein the increase is associated with a duration of an optical signal burst, wherein the blue-shift wavelength bias is a phase current defined by an equation I_(p)=f(t), and wherein I_(p) is the phase current, f(t) is a time-dependent function, and t is a time and ranges from 0 to an end of a burst mode time period.
 2. The method of claim 1, wherein dynamically compensating for the red-shift comprises: obtaining optical transmission power information based on real-time measurement of photo-current across a photodiode of the laser transmitter; estimating a burst mode time period according to received timeslot instructions; and calculating an injection current for use as the blue-shift wavelength bias to compensate for the red-shift based on the burst mode time period and the optical transmission power information.
 3. The method of claim 2, wherein calculating the injection current for use as the blue-shift wavelength bias is performed by an optical network unit (ONU) according to a media access controller (MAC) instruction.
 4. A method implemented in a passive optical network (PON) comprising: transmitting an optical signal in the PON via a laser transmitter utilizing time and wavelength division multiplexing (TWDM); and dynamically compensating for a red-shift in a wavelength of the optical signal associated with an increase in temperature of the laser transmitter associated with a duration of an optical signal burst, wherein compensation is performed by introducing a blue-shift wavelength bias to the laser transmitter, and wherein dynamically compensating for the red-shift comprises: obtaining optical transmission power information based on measurement of photo-current across a photodiode of the laser transmitter; estimating a burst mode time period according to received timeslot instructions; calculating an injection current for use as the blue-shift wavelength bias to compensate for the red-shift based on the burst mode time period and the optical transmission power information; receiving an electrical data signal associated with the optical signal, the electrical data signal comprising a data signal current; combining the data signal current with the injection current to create a combined current to dynamically bias the laser transmitter to compensate for the red-shift; converting the combined current into the optical signal via the laser transmitter, and transmitting the optical signal via the laser transmitter.
 5. The method of claim 4, wherein obtaining the optical transmission power information comprises: receiving a real-tune measurement of laser optical power monitor photodiode current represented as a digital value; and calculating the optical transmission power information from the real-time measurement.
 6. The method of claim 3, wherein the laser transmitter comprises a distributed Bragg reflector (DBR).
 7. The method of claim 6, further comprising applying a current to the DBR to provide wide-range wavelength tuning that complements the blue-shift wavelength bias.
 8. The method of claim 3, wherein the red-shift is proportional to an optical signal burst duration and an optical output power level.
 9. The method of claim 3, wherein the injection current varies proportionally to a transmission burst length.
 10. The method of claim 3, wherein the blue-shift wavelength bias approximately cancels the red-shift such that output of the laser transmitter is within 0.1 nanometers (nm) of a preferred output value.
 11. An optical component comprising: a laser transmitter comprising a phase section and configured to transmit an optical signal in a passive optical network (PON) utilizing time and wavelength division multiplexing (TWDM); and a media access controller (MAC) coupled to the laser transmitter, wherein the MAC is configured to dynamically compensate for a red-shift in a wavelength of the optical signal by: obtaining optical transmission power information based on measurement of a photo-current across a photodiode of the laser transmitter, estimating a burst mode time period according to received timeslot instructions, calculating an injection current for use as a blue-shift wavelength bias to compensate for the red-shift based on the burst mode time period and the optical transmission power information, and introducing the blue-shift wavelength bias to the phase section, wherein the red-shift is associated with an increase in temperature of the laser transmitter, and wherein the increase is associated with a duration of an optical signal burst.
 12. The optical component of claim 11, further comprising a receiver configured to receive an electrical data signal associated with the optical signal, wherein the electrical data signal comprises a data signal current, and wherein the MAC is further configured to further dynamically compensate for the red-shift by: employing a bias controller to combine the data signal current with the injection current to create a combined current to dynamically bias the phase section to compensate for the red-shift; converting the combined current into the optical signal; and transmitting the optical signal via the laser transmitter.
 13. The optical component of claim 12, wherein obtaining the optical transmission power information comprises: receiving a real-time measurement of laser optical power monitor photodiode current represented as a digital value; and calculating the optical transmission power information from the real-time measurement.
 14. The optical component of claim 12, wherein the laser transmitter is a Distributed Bragg reflector (DBR).
 15. The optical component of claim 14, wherein the DBR is configured to receive a current to implement wide-range wavelength tuning that complements the blue-shift wavelength bias.
 16. The optical component of claim 12, wherein the injection current varies proportionally to a transmission burst length.
 17. The optical component of claim 12, wherein the blue-shift wavelength bias approximately cancels the red-shift such that output of the laser transmitter is within 0.1 nanometers (nm) of a preferred output value.
 18. The optical component of claim 12, wherein the optical component is an optical network unit (ONU) configured to couple to a time and wavelength division multiplexed passive optical network (TWDM-PON).
 19. The optical component of claim 12, wherein the optical component is an optical network terminal (ONT) configured to couple to a time and wavelength division multiplexed passive optical network (TWDM-PON).
 20. The method of claim 1, wherein the blue-shift wavelength bias is independent of a duty cycle.
 21. The method of claim 1, wherein the dynamically compensating occurs during the transmitting.
 22. The optical component of claim 11, further comprising a receiver configured to receive an electrical data signal associated with the optical signal, wherein the electrical data signal comprises a data signal voltage, and wherein the MAC is further configured to further dynamically compensate for the red-shift by: employing a bias controller to create a combined signal based on the data signal voltage and the injection current to dynamically bias the phase section to compensate for the red-shift; converting the combined signal into the optical signal; and transmitting the optical signal via the laser transmitter. 